I have been curious of how much the NCR control Nevada. Vault City and New Reno is at http://en.wikipedia.org/wiki/Western_Nevada. So it is now 2281. How much control does the NCR have over Nevada?

The bear controls all of Nevada I heard.

But that's only what i've hear, just talk.
As for Reno, and vault city, I couldn't say.

Maybe someone else has said.

The bear is very annoying.

If my anolysis is correct, which I give a 33% probability thereof...

NCR controls all of California, parts of Oregon, and is pushing south into Baja and will expand into Canada once it has secured Oregon. Bear can't help itself, must consume.

As for Nevada itself, my interpretation is that NCR controls most of it, but for whatever reason, the Long 15 through New Vegas is the only practicible route East in Nevada. The Big Empty cuts off travel from the South(suspect that southern train tunnel links to it, well not in-game but in-universe) while the wreckage of the Divide stops going West from the Mojave without taking the Long 15.

Going further north or south is impractical due to limited established roads. Just my 2 cents.

They only own a bit of Nevada, not all of it as Lando said.

The Divide and the Big Empty block all colonization to the east, besides the New Vegas area, so they pushed north and south instead (that's why they go from Oregon to Baja).